Along with resent requirements for reductions of size and weight of a sliding unit, a phenolic resin molding material containing a glass fiber as a main filler is used in place of a metal material.
A phenolic resin molding material which contains a glass fiber as a filler, and in which a blending amount of a glass fiber is increased has sufficient property as a material replacing a metal material in terms of a heat resistance, dimensional stability, and strength. However, an abrasion resistance is prone to reduce with increase in an addition amount of the glass fiber, which makes it difficult to apply the phenolic resin molding material to a case requiring the abrasion resistance.
When a glass fiber is added so as to secure the strength of a molded article, the surface of the molded article is abraded by abrasive powders generated from the glass fiber crushed due to abrasion, sometimes resulting in increased surface irregularities and reduced abrasion resistance.
Then, many attempts have been made to improve the abrasion resistance of the phenolic resin molding material containing a glass fiber as the filler.
For example, Patent Document 1 discloses an invention of a resin pulley containing a novolac phenolic resin as a base resin and containing a glass fiber and glass bead as the main fillers. Patent Document 2 discloses an invention of a phenolic resin molding material containing an aramid fiber, a glass fiber, and a glass powder as the main fillers. Patent Document 3 discloses an invention of a phenolic resin molding material containing a glass fiber as the main filler and containing an organic natural material and a lubricant for improving the abrasion resistance.
However, because the above-mentioned phenolic resin molding materials each contain a glass fiber as the main filler, the materials have not met the latest requirement of further improving the abrasion resistance.
Therefore, in order to improve the abrasion resistance, there has been invented a molding material, which contains, in addition to a main component, various substances and further various lubricative substances (a friction modifier and a solid lubricant) in order to control the dynamic friction coefficient of the surface or to smoothen the surface.
Patent Document 4 reports a use of a carbon fiber whose crystal structure is an onion structure [e.g., PAN (polyacrylonitrile) base]. However, the abrasion resistance is insufficient, despite that the mechanical strength is improved.
Patent Document 5 discloses an improvement of an abrasion resistance by adding graphite, and Patent Document 6 discloses an improvement of the abrasion resistance by adding black lead. However, the addition thereof has a disadvantage in that the mechanical strength is reduced.
As described above, the improvement of the abrasion resistance is attempted, but it is extremely difficult to maintain a high abrasion resistance without reducing the mechanical strength.
Patent Document 7 discloses an invention of a phenolic resin molding material, which uses a glass fiber and wollastonite as the main fillers and contains an organic natural material and graphite.
Patent Document 8 discloses an invention of a molding material having an abrasion resistance and containing calcined clay. Patent Document 9 discloses an invention of a molding material having an abrasion resistance and containing a polyimide powder and pulp powders.
Patent Document 10 discloses an invention of a molding material which is obtained by adding a fluororesin powder and a polyethylene powder to a thermosetting resin. Patent Document 11 discloses an invention of a phenolic molding material containing graphite.
When a lubricative substance is added to a resin, the processability and moldability at the time of production sometimes decrease due to slipping property of the lubricative substance itself. Thus, the addition amount of the lubricative substance to a molding material is limited.
Moreover, when the addition amount of the lubricative substance increases, close adhesion with a resin decreases, and the mechanical strength of the molding material may decrease in some cases.
Therefore, in order to improve the abrasion resistance, a technology of reducing the addition amount of the lubricative substance and efficiently demonstrating an abrasion resistance effect has been demanded.
Further, as a recent requirement to a metal-replacement resin for sliding units of automobiles, industrial machines, etc., further improvement in the abrasion resistance and cost reduction have been desired.
Patent Document 1: JP 06-45200 B
Patent Document 2: JP 04-371807 A
Patent Document 3: JP 10-53692 A
Patent Document 4: JP 11-80501 A
Patent Document 5: JP 09-194685 A
Patent Document 6: JP 2004-204031 A
Patent Document 7: JP 08-101446 A
Patent Document 8: JP 08-319399 A
Patent Document 9: JP 07-157633 A
Patent Document 10: JP 2000-273321 A
Patent Document 11: JP 07-157633 A